1. Field of the Invention
The invention relates to a semiconductor light-emitting device and a fabrication method of the same. More particularly, the invention relates to a semiconductor light-emitting device in which a semiconductor light-emitting structure can be formed on a transparent single-crystal substrate such as a sapphire substrate, and a fabrication method of the same.
2. Description of the Related Art
A semiconductor light-emitting device for emitting blue light is widely known which uses nitride semiconductors such as GaN, GaAlN, InGaN, and InAlGaN (hereinafter, referred to as GaN compound semiconductors). A blue light-emitting diode (LED) that is covered with a wavelength conversion layer containing a fluorescent material can emit white light that can be used for lighting.
A GaN semiconductor layer is usually formed or grown on a sapphire substrate that is an insulating transparent single-crystal substrate. Thus, it is typically necessary to draw electrodes of the LED from a surface of the LED that is opposite to the sapphire substrate. Light is emitted in all directions. Light output from the LED can also be obtained from the sapphire substrate side.
In recent years, output capabilities of LEDs has increased and the market for LEDs has expanded from a display field where the LED is conventionally used to fields of lighting such as special lighting, general lighting, and automotive lighting. Simultaneously, the die size of LEDs has increased from about 300 μm square to 1 mm or 2 mm square. However, problems of uneven emission of light, impairment of current supply, heat generation in the LED, and the like have become obvious with the increase of the die size.
Japanese Patent Laid-Open Publication No. 2002-270905 proposes that a plurality of light-emitting elements be formed on a sapphire substrate and that the sapphire substrate with the light-emitting elements be mounted via bumps on a single sub-mounting element that is formed by a silicon substrate. Accumulation of a plurality of light-emitting elements can provide a large amount of light emission. The use of a silicon substrate that has better heat dissipation property than a sapphire substrate accelerates heat radiation, thereby preventing lowering of the luminous efficiency caused by heat generation. Thus, the luminous efficiency can be improved and an excellent light source for lighting can be obtained.
Japanese Patent Laid-Open Publication No. 2003-110148 proposes another semiconductor light-emitting device. In this semiconductor light-emitting device, a sapphire substrate on which a semiconductor light emitting device is formed is mounted on a mounting board with bumps for electric conduction and electrically-insulated dummy bumps interposed between the sapphire substrate and the mounting board, thereby improving the heat dissipation property.
Japanese Patent No. 3136672 proposes the following structure. An i-type GaN semiconductor layer doped with p-type impurities is formed on an n-type GaN semiconductor layer. One of the electrodes is formed on a surface of the i-type GaN semiconductor layer and a region surrounding the one electrode is etched. The other electrode is formed such that it surrounds the one electrode in all circumferences of that structure including side faces. In that structure, a current flowing between the electrodes is made to be uniform and light that is emitted laterally is also reflected so as to exit.
Japanese Patent No. 2914065 proposes a GaN light-emitting diode in which an insulating protection layer is formed on a semiconductor layer between a pair of electrode layers, thereby preventing a short-circuit caused by silver paste that is used for connecting a lead electrode.